1. Field of the Invention
This invention relates generally to methods and apparatus for the containment and treatment of wastewater and particularly to the use of superabsorbent polymers for the containment and treatment of wastewater.
2. Description of the Prior Art
Superabsorbent polymers (SAPs) are compounds capable of absorbing water and swelling to many times their original size and weight. SAPs generally absorb from about 100 to 1000 times their weight in water and some SAPs absorb up to 1500 times their weight in water. SAPs have many uses, e.g., as absorbing compounds in diapers and incontinence products, for protecting power and communication cables from moisture, in agriculture to increase the capability of soil to retain moisture and nutrients, and in the hygienic packaging of food products. SAPs are typically used alone in granular or powder form or in a composite form in which SAP particles are imbedded in pads or similar devices to enable easy handling and convenient use.
In general, these SAPs are wide-mesh cross-linked, water-insoluble polymers based on alkali metal salts of polyacrylic acid or copolymers of alkali metal salts of acrylic acid and acrylamide that are obtained by radical-initiated copolymerization of acrylic acid and polyfunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diallylether, butanediol acrylate, hexanediol methacrylate, polyglycol diacrylate, trimethylol propane diacrylate, allyl acrylate, diallyl acrylamide, triallylamine, diallylether, methylene bis-acrylamide, and N-methylol acrylamide. There are also SAPs based on hydrolyzates of graft copolymers of acrylonitrile on starch and on cross-linked starch/acrylic acid graft copolymers in which the carboxyl groups are partly neutralized.
While there are various types of SAPs known in the art, polyacrylic acid type SAPs are most often used for dewatering operations. Polyacrylic acid type SAPs are polymers containing an acrylic acid monomer unit of at least 50 mol % and are substantially water-insoluble while being highly absorbent and swellable for water. Such polyacrylic acid type SAPs include polyacrylic acid cross-linked polymers or copolymers, starch-acrylonitrile grafted polymer hydrolyzates, starch-acrylic acid grafted cross-linked polymers, and vinyl acetate-acrylic ester copolymer saponified products. In these polymers and copolymers, 60 to 90 mol % of the carboxyl groups thereof generally have their hydrogen atom substituted with an alkali metal.
Many SAPs are well known in the art. For example, U.S. Pat. No. 5,883,158 discloses a process for producing a SAP that absorbs up to 1500 times its weight in water. U.S. Pat. Nos. 5,567,779 and 5,496,890 disclose acrylonitrile based SAPs that absorb up to 1000 times their weight in water. U.S. Pat. No. 5,453,323 discloses a superabsorbent polymer having superior dryness that is made from acrylic acid and a cross-linking agent polymerized under controlled conditions. U.S. Pat. No. 5,451,613 discloses a carboxylic containing superabsorbent polymer having improved absorption rates and absorption under pressure. U.S. Pat. No. 5,684,106 discloses a particulate superabsorbent polymeric material which is a partially neutralized polymer of an ethylenically unsaturated carboxylic monomer cross-linked by a triethylenic or higher ethylenic cross-linking agent. Similarly, U.S. Pat. No. 4,511,477 discloses cross-linked polymers containing polymerized acrylamide and sodium 2-acrylamide-2-methylpropane sulfonate and their use to remove acidic water from fuels.
Wastewater is water containing dissolved and suspended contaminants. Wastewater comes in many forms. Wastewater can be sewage in the form of human or animal waste (human or non-human), effluents from food processing and canning operations, runoff from mining operations, radioactive wastes, hazardous wastes, or industrial waste from manufacturing operations. Wastewater is used herein to mean all such water based industrial and animal wastes.
The disposal of wastewater is a major problem throughout the world. Wastewater must be contained or controlled so that it does not pollute aquatic habitats for plants and animals and does not contaminate drinking water. In most instances, wastewater cannot be disposed of until the contaminants have been reduced to a level acceptable to governmental organizations, e.g., the Environmental Protection Agency. For radioactive and other hazardous wastes, there is no acceptable level for disposal. The wastewaters must be contained and the contaminants removed before disposal.
Wastewaters from animal rearing and production facilities are a major cause of air and water pollution. Ammonia is a common cause of odor in animal rearing and production facilities, particularly swine rearing facilities. The accumulation of manure and urine in these wastewaters results in the production of ammonia gas from ammonia volatilization and causes elevated levels of ammonia gas in the atmosphere. Accumulation of ammonia gas causes loss of production by the animals and causes respiratory problems for the animals. Ammonia can also accumulate around wastewaters from food processing and similar facilities.
Similarly, the disposal of wastewaters containing manure, urine, milk, feed, and the like is of great concern. Nutrients and other materials found in wastewaters containing animal waste contaminate ground and surface waters and contribute to eutrophication. Use of untreated agricultural wastewaters as fertilizers has proven problematic because of biological contaminants in the wastewaters. Also, the cost of transporting untreated wastewaters is very high since most of the cost is associated with transporting the water that makes up a large portion, usually greater than 95%, of the waste. There exists, therefore, a need for methods and apparatus to control the odor caused by wastewaters and methods and apparatus for treating wastewaters to manage the excess nutrients in many wastes, particularly if the nutrients can be reused as a fertilizer.
The containment and treatment of wastewater is often a major cost associated with a business enterprise. Much effort has been devoted to developing methods and apparatus for containing and treating wastewater in an economical way, e.g., using as little energy as possible, reusing materials and energy if possible, and minimizing the amount of solid waste. Despite this effort, however, there exists a continuing need for new methods and apparatus for economically and efficiently containing and treating wastewater and for managing the byproducts of such treatment methods.
It is, therefore, an object of the invention to provide new methods and apparatus for the containment and treatment of wastewater.
It is another object of the invention to provide new methods and apparatus for producing fertilizers and fertilizers produced by such methods.
It is a further object of the invention to provide new methods and apparatus for controlling odor caused by ammonia in wastewaters.
It is another object of the invention to provide new methods and apparatus for generating cool air utilizing the evaporation process involved with treating wastewaters.
These and other objects are achieved by using superabsorbent polymers (SAPs) for the containment and treatment of wastewaters. The SAPs absorb substantially all of the wastewater and prevent it from leaving a defined containment area. Once contained, the water can be evaporated from the SAP to produce a substantially dry polymer composition containing the SAP and the wastewater contaminants. The dry polymer composition can be discarded or, when appropriate, used as a fertilizer for plants and other vegetation. Advantageously, the SAP reduces the odor associated with ammonia containing wastewaters by binding to the ammonia and reducing the ammonia gas present in the airspace around the wastewater. The evaporation process may be conducted in the presence of a heat exchanger to produce cool, fresh air that can be collected and used to cool facilities, particularly animal rearing and production facilities.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments that follows.